Demosthenes

it is a Feynman diagram, a vacuum diagram is just a specific name for a particular type of diagram.

To Answerer:

It depends on how you're seeing the proton/antiproton creation. It's my understanding that if the particle pairs appear out of nowhere, then the ceation can be represented by a vacuum diagram, named because the beginning and the end of the diagram are just a vacuum. If you were to draw one, you'll get a circular shape. As for the particle that moves backward, apparently in case of proton and antiproton, it's a photon.

[ August 10, 2002: Message edited by: Demosthenes ]</p>